The invention herein relates generally to an electrophotographic recording method and apparatus especially capable of recording micrographic images as high resolution positive or negative transparencies. More particularly the method and apparatus is embodied in a camera-processor that employs high resolution electrophotographic techniques to form a permanent image-carrying transparency suitable for mounting in a storage card, for example, the invention enabling the transfer processing to be carried out in normal light, and with unusual speed over known micrographics duplicator apparatus.
Micrographics is a general term used to denote the creation or use of information communication or storage medium containing images too small to be read without magnification, typified by microfilm. The micrographics may be reduced images of printed or other graphics, graphical design and the like for storage in the printed form and enlargement for printing or projection retrieval.
Conventionally the art of micrographics employs photographic technique using silver halide emulsion photographic film. Conventionally the photographic film is of high speed, fine grain, expensive both as to the value of their inherent silver content and in the processing technique required. Grain size, contrast, fogging are limiting factors in photographic reproduction of this type. The techniques of micrographics require fine grain photographic film in view of the substantial reduction in the size of the image and the substantial enlargement required for viewing as by projection or copying.
Photographic film of the type required generally require expensive chemicals and processing, as well as expenditure of time to process the exposed film to its usable form. Additionally photographic film, until exposed and developed, is light sensitive and often bulky, requiring special handling through processing and storage.
The conventional silver halide film of 140 microns thickness has an emulsion which is about 20 microns thick. The conventional silver halide film is thus not easily flexed without damage. Its resolution is determined by the size of the silver grains; the bigger the grain, the faster the film. In production, the film cannot be inspected in ordinary light, it cannot be handled or transported except in special dark packages. The emulsion is soluble in ordinary liquids and is hygroscopic.
Conventional photographic microfilm is not capable of being re-exposed for adding information. The inherent chemical nature of silver halide films results in an irreversible chemical change when the microfilm is exposed, even prior to the wet development process.
Electrostatic techniques such as xerography and electrofax processes as they are commonly-known are not readily adaptable to the production of micrographics or microfilm transparencies. Inherently, the familiar electrostatic processes are not adaptable for use in high speed photographic applications.
Known micrographics processsors employ photographic technique and film such as silver halide emulsion photographic film as the reproductive medium. Photographic film which forms the transparency is expensive and the time required for processing the film to the final form as the transparency is an undesirable factor of the known processors. Additionally, the photographic film requires special handling and storage in a light-tight container.
The most familiar xerographic process of the present time utilizes a large metal drum coated with amorphous selenium as the photoconductive member. The photoconductive member has extremely low gain and is very thick, of the order of a fraction of an inch, in order to be able to build up a sufficient charge to enable toning. Low surface potentials during charging require longer toning times. The process performed is complex, occurs in a complicated and expensive machine, and the speeds, resolution and flexibility of such machines and the processes thereof leave much to be desired. Electrofax equipment of the present time utilize zinc oxide coated conductive paper which is charged, exposed, led through a toner bath and fused. The photoconductive gain is again low, the resolution crude, the gray scale short and limited, the equipment complex and bulky.
Inherent faults with the known methods, apparatus and the photoconductive materials and articles used have prevented use in such fields as high resolution micrographics, high speed photography, and many other technical areas. Record-keeping, by means of projectable microfilm is a field wherein there is a long-felt need for a process for making the image-carrying transparency quickly, with high resolution, economically, with simple apparatus and having the ability to withstand long periods of storage.
Accordingly, it would be highly desirable to provide a method and apparatus for making an image-carrying transparency in which the transparency material is significantly less expensive and easier to handle, i.e., not light sensitive, having improved flexibility, etc.
Additionally, it is desirable to reduce processing time and eliminate expensive processing chemicals. Of considerable importance would be the capability to change or add to the developed microfilm.
The invention herein eliminates the expensive film and many processing steps while providing an improved recording that is effective for its intended use and importantly having the capability of altering the recording to add information from time to time without adversely affecting the information which is already contained thereon.